Bearings are the devices, which facilitates relative motion (rotation) between two objects. In a typical construction, bearings are attached to a shaft through the bore and housing around its outer diameter. Bearings are designed to tolerate different loading conditions depending upon its type. Ball bearing and Roller bearing are the two most commonly used bearings in the engineering industry. Ball bearings are widely used for their simple design as they contain ball (spherical in shape) of various configuration as their rolling element. Roller bearings contain rollers, which are cylindrical shaped objects, as their rolling element. Roller bearings may contain rolling elements that have a large aspect ratio (length/diameter), small aspect ratio, spherical shape, or a tapered shape. The use of roller bearing has substantially increased in moderate and heavy duty applications, wherein the load bearing capacity is substantially high and it requires long durability as well as high efficiency.
The roller bearing plays a vital role in transferring the rotational force from one shaft to another. It acts as a connector, which facilitates the collinear motion of the shafts in all the planes. While in operation, due to the heavy loads and other application conditions, the probabilities of misalignment of shaft are very high. Due to such misalignment, the effective length of the contact area of the roller element gets reduced, which in turn creates stress on the roller element causing significant wear and tear. The misalignment can be either offset or angular, which can be checked and maintained by balancing the tolerance level of the rotating elements of the roller bearings. The wear and tear of a roller bearing includes cage deformation, roller bending or skewing and a wide range of surface defects. The latter include etching, coarse and fine grain spalling as well as brinelling. It is essential to check such wear and tear and to modify the existing geometry of the roller bearing to the extent that it can optimally reduce the stress on the contact surface of the roller bearing.
Conventional cylindrical roller bearing construction uses inner and outer racetracks that are essentially straight in profile. In order to allow for angular displacement between these racetracks due to misalignment and/or deflection due to loading, the rolling elements are profiled at their ends to reduce the contact stresses. Basically this tapering minimizes “pinching” of the rolling elements at their ends. While this solves the basic issue it does mean that the contact length between the rolling elements and the racetracks will always be shorter than the optimum for minimal contact stress and maximum bearing fatigue life.
With the advent of technology several attempts were made to modify/improve the geometrical construction of the bearings so as to make them more durable and efficient. One such prior art, discloses a controlled contact stress roller bearing. In the said prior art, rollers with cylindrical configuration without substantial end relief are positioned between the outer and inner raceways. The said rollers apply a contact force distributed over the outer raceway and inner raceway contact areas, resulting in an outer and inner raceway maximum contact stress, which determines respective outer raceway life and inner raceway life. The outer raceway has a crowned configuration such that a calculated maximum contact stress over the outer raceway contact area is controlled with respect to the maximum contact stress over the inner raceway contact area in order to make the outer raceway life substantially equal to the inner raceway life. However, the prior art does not teach the optimization in the geometrical construction of the roller bearing to reduce stress on the contact surface area under all operating conditions thereby increasing its life span.
Another prior art discloses a roller bearing with curved race track and roller profiles, whereby the radius of curvature is substantially bigger than the biggest distance between the center axes of the race tracks and their envelope surfaces, and having a cage for the rollers. Said cage is designed to permit required axial displacement of the rollers at tilting of the race tracks relative to each other. However, the same does not disclose the method to adjust the length of the roller depending upon the operating condition.
Yet another prior art discloses a roller bearing with specially constructed rollers. In the said prior art, the roller bearing have an outer and an inner race. The rollers between the races have a specifically constructed longitudinal external surface. The roller has varying diameters and varying radii of curvature along its length. The diameters are functions of the contact stress along the roller, the length of the roller, any contact angular misalignment of the roller axis in relation to the inner race axis, and the effective diameter of the bearing. The varying diameters are also such that within an acceptable error limit, a uniform contact stress is placed on each roller along the length of the roller. If desired, instead of the rollers, the inner race outside surface, or the outer race inside surface may be shaped to cause the uniform contact stress. However, the said prior art does not discloses the mechanism to enhance the stress bearing capacity without modifying the roller bearing.
To overcome the limitations discussed above and several others, the present invention discloses a roller bearing with modified geometry to optimize the stress level thereby increasing its durability and efficiency.